One common still camera shutter construction with which the present invention is concerned utilizes a pivoted shutter member which is spring urged into a position where it covers the camera lens aperture. A shutter actuation member is movable between a released position to which it is urged by spring, and a cocked position where it is held by a latch until a shutter actuation release button is depressed by the user to take a picture. As the shutter actuator is thereby released, it strikes and moves by a projecting portion of the shutter member which swings back and forth to momentarily uncover the lens aperture.
The shutter actuator is then cocked by movement of a film advancing thumb wheel or lever which rotates a member which performs both a shutter actuator cocking and one-frame film advancing operation. Usually, the cocking operation occurs during the initial portion of the film advancing operation. A variety of means have been provided to prevent accidental tripping of the shutter actuator before the film is fully advanced. This serves to prevent accidental double exposure of a portion of the previously exposed film frame.
The necessity for this feature arises from certain mechanical constraints which generally require that the shutter actuator release mechanism be restored to a cocked position substantially before the termination of the film advancing process. This is necessary to achieve proper synchronization of the two processes. In inexpensive cameras the flip-open shutter described is probably the most commonly employed shutter type. The shutter release system for such a shutter frequently consists of a linearly operable slider spring-urged to a released position as described. The film advancing mechanism is coupled to force the slider during film advance against the biasing action of the spring involved to a point where it is engaged by the latch. Upon depression of the shutter actuator release button, a coupled motion therefrom trips the latch to a disengaging position, whereupon the slider is rapidly actuated by this spring in a linear direction to an opposite extreme position thereof, during the course of which travel a striker attached to the slider impacts upon some portion of the shutter as described.
Because of the above-mentioned constraints, it is found necessary to provide a measure of substantial further film advance after shutter actuator slide cocking is complete, during which interval the slider is vulnerable to premature tripping. Although a great many systems have been devised to prevent this premature shutter tripping, such prior art systems of which the applicant is aware generally require the addition of extra components to the camera, thereby adding to camera cost. It would be a useful feature if such a simple reciprocating slide system could be modified at little or no cost to provide such a feature.